Removing scratches from a GLASS dome port

Hi all,I have a Subal glass dome with a scratch in it that definitely affects the images more that I can ignore so looking to see if there is any agreed upon DIY approach.

To be exact it is not as much a scratch as it is an abrasion of what I suspect is the coating. The result is a triangularly shaped rough and matte patch around 5 mm wide. When shooting just a bit against the light, the reflection of the patch shows up in the image as a blurry patch in the image. I can not afford a replacement dome but am willing to try to fix it myself. Or perhaps take it to an optician or someone else. If anyone has good advice let's try to compile it here.

I read through the amazingly helpful thread on what to do with scratches in acrilyc domes. I found two posts that dealt with glass domes and have taken the liberty to copy-paste them here. I was wondering if the original posters (or others) can tell me more about their final results - I am particularly worried about losing coating once I start this process, though losing the roughed up coating due to the abrasion is probably needed and better than what I have now, I am wondering whether the transition to the unharmed areas of the dome will be smooth and whether the uncoated, but at least polished patch, will show up in images afterwards?

From Yellowmon on June 20, 2009:Glass port scratches are as problematic as they are inevitable. Fortunately, it is possible to remove scratches in glass ports if the scratches are not too deep. Stephen Frink suggested to me I use "jewellers rouge" which I found on Amazon. I used a Dremel which has a power cord (when I tried with battery packs, ran out of juice before finishing) and a whole bunch of felt polishing wheels (catalog #414). It took a long, long, long time. Perhaps an hour but the minor scratches did disappear. I went through a number of felt wheels. It is a long and boring process but gives one time to reflect on the dangers of rocks attacking poor defenseless dome ports and to be more protective in the future. I write this now as I am preparing to attend to another session of polishing, which I hate as much, if not more, than cleaning the camera's sensor (also necessary this weekend). While you are out diving and having fun, think of a tiny wheel spinning round and round and be thankful if you have acrylic domes how much easier they are to repair.

I can't guarantee this process will work for everybody but so far it has done well for minor, hairline scratches and little dings. I hope this advice cuts into the sale of replacement Seacam domes, Harald is doing far too well these days.

Good luck!

From Kogia, August 18, 2009:I had been told by opticians and housing manufacturers that it is not possible to polish out scratches from glass domes: they must be replaced. However, after reading this post, I did some searching online, and found a DIY Glass Polishing Kit for $40 at www.hobbytool.com. I had a couple of scratches on my glass dome that were not deep, but close to 2cm long, and managed to produce really ugly black scars on the image files when shooting into the sun. To my utter astonishment, they disappeared after only about 20 minutes of polishing using an electric drill with the wheel, pad, and polish solution provided in the kit. Best $40 I ever spent. Thank you Yellowmon!

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Here are some images of the worst of the abrasions/scratches on my dome(reflection is of same patch on underside of glass dome):

Thanks! I didn't remember seeing those last two. I just ordered the kit mentioned in the last one - only $35!

BTW, post photos of that spot on your dome port (if you can still find it ) after repairing it. The scratch in mine is more of a straight-line gash, rather than the rash-type scratch you've got. I hope it works (for BOTH of us)!

Bruce Yateswww.UnderwaterReflections.com
Canon 5DMkII in Aquatica, 1DsMkII in Seacam, G15 in RecSea...Inon Z240's...too many lenses"If at first you don't succeed, try, try again. Then quit. No use being a damned fool about it." WC Fields

Kevin at www.aquaphot.com can polish out scratches in glass. Be aware (I have found out the hard way) that the problem when polishing out scratches is that they act very much in the same way as when using a marking cutter when cutting sheet glass - its a stress point where a fracture can occur. If you overheat the glass whilst polishing - its hard and requires a lot of polishing - then it can shatter - I know!

...If you overheat the glass whilst polishing - its hard and requires a lot of polishing - then it can shatter - I know!

Good point, Paul! That would suggest polishing a little, waiting a minute, polishing a little more, and so on...a good job to do while watching TV!

Bruce Yateswww.UnderwaterReflections.com
Canon 5DMkII in Aquatica, 1DsMkII in Seacam, G15 in RecSea...Inon Z240's...too many lenses"If at first you don't succeed, try, try again. Then quit. No use being a damned fool about it." WC Fields

Don't know about glass domes, but in the eyeglass business you cannot polish out a scratch on a glass lens. There are several reasons for this. First the outer layer of a glass lens is tempered. The surface is under greater pressure than the interior of the lens. If you have a deep enough scratch you continuously have fine little flakes coming off of the edges. Second there are multiple layers of optical coatings to reduce aberrations. If you polish a lens you remove these coatings selectively in the area that you polish.

If you polish a glass dome you may run into the same problems. I would recommend as little polishing as possible. Just enough to reduce the edges of the scratch so they are not as obvious. Another approach is to use a compound that will fill in the scratch. I have read of such compounds, but can come up with no names.

Laminated car windscreen repairers inject a resin (some kind of cyanoacrylate?) under vacuum. A resin with the same refractive index as glass would be great. Anyone know which clear resins have the closest refractive index to glass?

Hi Bruce,I think you will get to it before I do. I am in China and wont have time to start working on the dome for the next month or two. I am thinking that no matter what, except for shattering the dome, I will be better off trying to repair it. Even if I do loose the coating, it should be better than what I have now. Alternatively, a resin or compound to fill in the scratch would be interesting as well. Let's keep this post alive to see if anyone has practical info on the latter approach and of course I would love to hear about your experience with the glass polishing kit.

No, David, I got it from the place referenced in your last quote: www.hobbytool.com

Bruce Yateswww.UnderwaterReflections.com
Canon 5DMkII in Aquatica, 1DsMkII in Seacam, G15 in RecSea...Inon Z240's...too many lenses"If at first you don't succeed, try, try again. Then quit. No use being a damned fool about it." WC Fields

I think they must have changed their name or something. I didn't even notice, but now I see that when I type hobbytool.com, it takes me directly to the pjtool.com. If that doesn't happen to you please post the link you used.